Rami Abdelrahman of the Syrian Observatory for Human Rights quoted a spokesman for the "Martyrs of Yarmouk" rebel brigade as saying the convoy of Philippine peacekeepers were being held as "guests" in the village of Jamla, about one mile from a ceasefire line with the Israeli-occupied Golan Heights.

"He said they will not be harmed. But the rebels want the Syrian army and tanks to pull back from the area," Abdelrahman said after speaking to the rebel spokesman on Thursday morning.

Philippine President Benigno Aquino said the peacekeepers were being well treated and that the United Nations was in touch with the rebels to ensure their safety. "By tomorrow they expect all of these 21 to be released," he said, adding their release might occur as early as Thursday.

Aquino said both sides in the Syrian conflict considered the United Nations a "benign presence" in the country - a view not shared by many Syrian rebels, who hold the organisation at least partly responsible for a lack of international support.

In a video released to announce the capture of the U.N. convoy on Wednesday, a member of the Yarmouk Martyrs' Brigade accused the peacekeepers of collaborating with Assad's forces to try to push them out of village of Jamla which the rebels seized on Sunday after heavy fighting.

Peacekeepers of the U.N. Disengagement Force (UNDOF) mission have been monitoring a ceasefire line between Syria and the Israeli-occupied Golan Heights, for nearly four decades.